12AX7; the original specification for this family of high-gain dual-triodes. Maximum plate voltage 300V. RCA patented the tube in 1946 and began sales in 1947.
12AX7A; updated specification allows 10% higher plate voltage. This is the current design criteria and relevant tube number. A 12AX7A can be used to replace a 12AX7, but not the other way around. First use about 1954 (ref. GE).
7025; this is actually a 12AX7 with an American INDUSTRIAL part number. The 7025 designation indicates additional testing for low microphonics and low hum. Similarly, you would choose one of my Applications Graded TM GAIN tubes, which additionally would be tested for the greatest gain, burned in and listen tested in an actual amp with a specially optimized brutal high gain circuit! If it sounds like an Applications Graded TM GAIN tube is better, it is!
Application Graded TM; There are three different types of circuits in your amp that use 12AX7 tubes. There is the GAIN stage which is the most demanding in terms of sonic qualities, followed by the FUNCTION stage(s) which may or may not increase the gain of the signal but not by much, and then lastly the DRIVER stage which must have each triode within it operating at the same potential in order for you to benefit from those matched output tubes. By sorting the tubes for their best application the amplifier performs far better. Its tone is stronger, the sustain is longer and more natural, and each tube in the amp lasts longer! Hi-Fi tube amps are laid out much like a guitar amp, featuring gain stages and a driver stage. They also stand to gain from properly selected tubes. For other tube based equipment like expensive studio gear and tube foot pedals, a GAIN tube should always be selected.
Burn in; most electronic equipment including tubes will fail within the first 24 hours if it premature failure occurs at all. So to bring out failures, power is applied along with the typical load for a period of time (burn in time).
Clean; the ability of a tube to amplify a signal as designed without adding harmonic overtones.
Compression; In a word, punchy. Compression lessens the dynamic range. The quieter parts of your playing are made to sound louder by making the loudest parts quieter. For example your picking, plucking, swishing and single notes can be made to sound the same volume as a loudly played chord. Or the breath of a singer made to seem as loud as her voice. Technically when the tube runs out of headroom (ability to accept larger input signals while still resulting in proportionally larger output signals) instead of distorting the tube puts out a clean signal but the louder parts don't get represented by as loud of a signal as it otherwise would. If this sounds to you like it gets quieter, then you thinking right, however, the brain interprets the new softer loud part as being a louder soft part. In other words, compression makes the quieter parts of the sound seem louder. For example, a single note could be made to be as loud as a power chord. Tubes compress very naturally, unnoticeably until you learn to listen for it. Compressors deal with rigid predetermined levels for what happens and when - the compression ratio is how much the loud part gets squashed, the threshold is the level that has to be crossed before anything happens. In a tube the compression ratio changes with the amount that you exceed the threshold. In other words, dynamically. Another distinguishing difference is the release time. That's the part That's really hard to get right on a compressor, because it is the time it takes to fade to normalcy. In a tube you never can play in such a way as to hear that gating effect of the release. Tube compressors usually use tubes that are rich, dirty, and ill suited for its use. That's is because the compression brings up all the noise levels. Use a CLEAN COMPRESSED tube in your compressor if you can, to reduce the noise and allow some natural tube compression! Select PRIVATE STOCK for the best possible performance level.
Distortion; tubes either compress or generate harmonic overtones when asked to do more than the tubes' construction allows. In musicians language distortion refers to the latter, rich harmonic texture that is desirable and specific to the way that tubes distort. Technically, any variation in the signal other than amplification is distortion, which compression certainly is, but we do not hear compression as distortion. Instead, we regard the added overtones as obvious and use this definition in music-speak.
Driver; the last tube before the output tubes. In push-pull amps (almost every amp over 15 Watts) the output tubes should have matched performance, although there would be little point if the driver tube was not also matched. More on this and more on the about tubes page.
Dynamic Range; the ability to express yourself in terms of volume. Acoustic guitar for example can play to a maximum volume. That range of volume from the quietest to the loudest is the dynamic range. In electronics, you take into account the noise floor. When measured, this value is expressed in decibels.
ECC83; this is the European part number for the American 12AX7. They are in every way the same tube.
Gain; when the signal voltage comes out at a larger magnitude than it went in then it has gain. For example, the voltage from your guitar swings one tenth of a volt, and the voltage of the same guitar signal after being amplified by the first tube circuit will increase to maybe five volts! Now that is some gain! If the input is the same as the output then it has unity gain. You do have circuits in your amp near unity gain. A tube would really have to be messed up, or you would have to really be rocking the amp for a microphonic tube to be a problem when in a near-unity circuit! 12AT7's are very prone to high frequency microphonics, but due to their pingy tone they only find use in very low gain stages like the reverb driver or the output driver. Different tubes within a batch exhibit differing amounts of gain. The more "healthy" a tube is the more rigid it must be in its construction in order to be usable, ie; a tube may have so much gain that it exhibits an unusable amount of microphonics in a gain stage circuit, and still be perfectly suitable for use anywhere else in the amp.
GAIN/DRIVER; these are a bit hard to come by, and are an ideal choice for experimenters. You can use them as top performing gain stage tubes, or as balanced section Driver tubes equally well. One of these of each tube type make the ideal experimenters kit, as they can each be used anywhere in the amp. Offered at a slight premium.
Headroom; how loud your signal can be before you can expect its behavior to change. What happens when you run out of headroom in a tube is going to be harmonic distortion and or compression.
Microphonics; when the vibrations caused by amplified sounds cause an internal part of the tube to vibrate in sympathy resulting in a runaway effect similar to sticking a microphone in front of a speaker. All tubes are microphonic to some degree. In preamp tubes the problematic notes always tend towards the higher frequencies. In output tubes the tendency is towards low notes. Since preamp tubes and circuits have more gain, they are more likely to be a practical problem for the player. Most amps are laid out so that the input jack is closest to the tube whose circuit has the most gain. This first tube also imparts the greatest effect on the sound of the amp.
Noise Floor; how loud the noise level is when no signal is present.
Overtones; notes in addition to the fundamental one that is a product of the electronics and not necessarily part of the musical source.
PRIVATE STOCK; For a long time I would not sell these to anyone. They are truly the best tubes available of their type. Very few tubes make the grade. When you read about guitar legends who utilize a technician to hand pick the best tubes after listening to hundreds, THIS IS IT. That's what I'm doing, these are the tubes. Offered at an appropriate premium.
Punchiness; a sound quality similar to bassy response but relating to the ability to move a lot of air quickly. Like a punch in the chest.
Re-Amp; a recording technique where the instrumentalist is first recorded without the sound of an amp, then that is played back and recorded through an amplifier.